This invention relates to an operating force transmitting apparatus for transmitting the operating force exerted on a lever or pedal to an actuating member such as a brake or clutch.
The driving or operating control of construction vehicles includes the control of transmission of the power developed by the engine by engaging and disengaging a main clutch, the control of steering of the vehicle by means of a steering clutch and the control of braking the vehicle by means of a brake. Such operating forces are, in general, transmitted by a manually operated lever or pedal through an operating force transmitting arrangement including a mechanical linkage means to a main clutch, steering clutch or a brake.
The above-mentioned operating force transmitting arrangement adapted to be actuated by operating a lever or pedal is generally constructed to have a proper lever ratio so as to reduce the manual operating force. For this purpose, such operating force transmitting arrangement is usually provided with a mechanical toggle means or hydraulic booster.
The operating force transmitting arrangement designed to determine the operating force by a lever ratio without using the mechanical toggle means is advantageous in its simple construction and low cost, but suffers from the following disadvantages.
For example, in the case of the brake pedal, even if the pedal is depressed, because of the predetermined lever ratio and the increased idle stroke of the pedal caused by the weardown of the brake lining, it is difficult to render the brake operative. Also, even if the brake becomes engaged, it is difficult to keep it depressed.
Further, because the lever ratio remains unchanged irrespective of the stroke of the brake pedal, a large depressing force is required for actuating the brake. Stating in brief, since the stroke of the brake pedal and the stroke of the brake actuating member vary in a generally fixed relationship, it is necessary for the brake pedal to have an idle stroke corresponding to the idle stroke of the brake actuating member.
Therefore, it is necessary to step down the brake pedal over a large stroke until the brake is actuated, and when the brake becomes operative the brake pedal is moved away from the operator's seat so as to make the depression of the pedal difficult, and therefore the brake cannot be actuated satisfactorily and smoothly. Further, since it is impossible to increase the lever ratio during braking of the vehicle, a large depressing force is required.
Moreover, such arrangement is disadvantageous in that the stroke (or the lever ratio) of the brake actuating member cannot be varied optionally against the stroke of the brake pedal, and the depressing force cannot be changed optionally.
The operating force transmitting arrangement using the hydraulic booster can overcome the problems concerning the operating force and the operating stroke, however, is disadvantageous in that it is complicated in construction and expensive.